Hollow anode plasma reactor and method

ABSTRACT

The plasma processing apparatus includes a plasma chamber, a first electrode, a second electrode, and a plasma containment device. The plasma containment device has a plurality of slots and is electrically coupled to the first electrode. The containment device is configured to confine plasma within an inter-electrode volume while facilitating maximum process gas flow. When plasma is generated by applying electric fields to process gas within the inter-electrode volume, the containment device electrically confines the plasma to the inter-electrode volume without significantly restricting the flow of gas from the inter-electrode volume.

PRIORITY CLAIM

This application is a Continuation application of U.S. application Ser.No. 11/248,779, entitled “HOLLOW ANODE PLASMA REACTOR AND METHOD,” filedon Oct. 11, 2005, now abandoned which is a Divisional application ofU.S. application Ser. No. 09/859,091, now U.S. Pat. No. 6,974,523, filedMay 16, 2001, both of which are hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates to the fabrication of integrated circuits, andmore particularly, to an apparatus and a method that remove materialsfrom a surface.

BACKGROUND

A dry etch process may be used in semiconductor wafer processing toremove materials from a surface of a wafer, or from films deposited on awafer by exposure to plasma. Plasma is an electrically neutral,partially ionized phase of matter. An etch reactor not only producesplasma, but also provides a degree of control of the chemical andphysical reactions that occur on the wafer or film surface. Through theetch process, materials are removed from the wafer or film surface in anetching area to form profiles and dimensions that, in part, definecircuit elements.

In a known plasma reactor, the plasma is produced in a volume proximateto the wafer and expands to fill most or all of the total reactorchamber volume. The plasma interacts with all of the surfaces the plasmacontacts. Outside the proximate wafer volume, the plasma-wallinteractions can yield undesirable results such as a sputtering of wallmaterial or more commonly, a deposition on or near the wall. As walldeposits increase in thickness with continued processing, the walldeposits can flake off creating particle contaminants. Additionally,because the wall deposits can have different electrical and chemicalproperties than the wall itself, the deposits can change how the plasmainteracts with the wall and can cause a change in the plasma propertiesover time. The wall deposits must therefore be periodically removed.In-situ plasma cleaning is preferable, but often difficult or very slowdue to the low energy of some plasma-wall interactions. Thus, manualcleaning of the reactor is often required, which increases operationalcosts and reduces system throughput.

FIG. 1 illustrates a cross-sectional side view of a prior art plasmareactor. The apparatus employs a chamber housing 110 that forms areactor or chamber 100. Disposed within the top of the housing 110 is afirst electrode 112. As shown, the first electrode 112 and the housing110 are coupled electrically to ground 134. A second electrode 114 isdisposed within the lower part of the housing 110, opposite and parallelto the upper electrode 112. The second electrode 114 is electricallyisolated from the housing 110 by an insulator ring 116. A substrate orwafer 118 to be etched is placed on an interior face of the secondelectrode 114, which is often configured with a clamping device and/or acooling device. The wafer 118 is surrounded by a thin plate 120fabricated of an insulator material such as quartz.

Etchant gas is supplied to the reactor 100 by an etchant gas supply 122and a supply line 124. The supply line 124 is connected to the reactor100 via a port through the first electrode 112 to deliver an etchant gasto the interior of the reactor 100. A reduced pressure is maintainedwithin the reactor 100 by a vacuum pump 128, which is connected to thereactor 100 through a vacuum line 126. Radio Frequency (RF) power issupplied to the second electrode 114 by an RF power supply 130 and animpedance matching network 132.

At the appropriate reduced pressure of etchant gas within the reactor100 and the application of an appropriate RF power to the secondelectrode 114, a plasma is formed in the inter-electrode volume 146between the first electrode 112 and the second electrode 114, andexpands to the volume 142 outside the first and the second electrodes112 and 114. The plasma gas within the volume 142 can interact withexposed interior walls 144 of the chamber housing 110.

Others have attempted to confine plasma proximate to the wafer 118. Someknown devices employ two or more annular rings 150 immediately about theinter-electrode volume 146 between two parallel disk electrodes similarto those illustrated in FIG. 2. Added to the reactor 100 of FIG. 1 aremultiple annular rings 150 that fill the volume between the upperelectrode 112 and lower electrode 114 about their periphery. The annularrings 150 are fabricated from a non-electrically-conductive material,such as quartz, and have small gaps 152 between them. The gaps 152 allowgas to flow from the inter-electrode volume 146 to an outer volume 148,and then to the vacuum pump 128. The gaps 152 are sufficiently narrowand the width of the annular rings 150 sufficiently wide that there is asignificant loss of gas flow conductance through the small gaps 152.This gas flow conductance loss creates a pressure differential betweenthe inter-electrode volume 146 and the outer volume 148. The plasmacreated within the inter-electrode volume 146 is confined to theinter-electrode volume 146 due to the narrow gaps 152 and the very lowpressure that exists in the outside volume 148.

The above-described approach to plasma confinement can suffer from alimited processing window. At low plasma operating pressures, generallyless than 60 millitorr, the efficacy of the annular rings 150 cannotalways establish a beneficial pressure drop. In addition, in instanceswhere the plasma is confined, the low gas flow conductance created bythe annular rings 150 limit the gas flow rates that can be employed.

If a plasma can be confined to a volume proximate the wafer, severaladvantages are gained including enhanced process stability andrepeatability, and reduced system maintenance. Accordingly, there is aneed for an apparatus and a method that confines the plasma to a volumeproximate the wafer while not significantly restricting the pressuresand/or gas flow rates of the apparatus and method.

BRIEF DESCRIPTION OF THE DRAWINGS

In the figures, like reference numerals designate corresponding partsthroughout the views.

FIG. 1 is a cross-sectional side view of a prior art reactor.

FIG. 2 is a cross-sectional side view of a second prior art reactor.

FIG. 3 is a cross-sectional side view of a presently preferredembodiment.

FIG. 4 is a cross-sectional top view taken along line 2-2 of FIG. 3.

FIG. 5 is a flow diagram of FIG. 3.

FIG. 6 is a cross-sectional side view of an alternative presentlypreferred embodiment.

FIG. 7 is a cross-sectional side view of a second alternative presentlypreferred embodiment.

FIG. 8 is a cross-sectional side view of a third alternative presentlypreferred embodiment.

FIG. 9 is a cross-sectional top view taken along line A-A of FIG. 8.

FIG. 10 is a cross-sectional top view taken along line A-A of analternative presently preferred embodiment of FIG. 8.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

Presently preferred embodiments of the apparatus and method of thepresent invention described below confine a plasma to a volume proximatea wafer and minimize the surface areas with which the plasma interacts.Presently preferred embodiments further provide a high conductance forthe flow of gases out of an inter-electrode volume. The presentlypreferred apparatus and method utilize a confinement method thatsubstantially confines electric fields to a plasma region of a chamber.The presently preferred apparatus and method may be a unitary part of,or integrated within many plasma-processing systems. The presentlypreferred apparatus and method substantially minimize plasma-wallinteractions, reduce system maintenance, improve process stability, anddecrease system-to-system variations.

Referring to FIGS. 3 and 4, the apparatus preferably employs a chamberhousing 202 that forms a reactor or chamber 200. Disposed within a topportion of chamber housing 202 is a first electrode 210. In onepresently preferred embodiment, the first electrode 210 can have a discshape and can be made of silicon (Si) or silicon carbide (SiC),preferably having a resistivity of less than 1 ohm/cm. The firstelectrode 210 and the chamber housing 202 are electrically coupled toground 254. A second electrode 220 is disposed within a lower portion ofthe chamber housing 202, opposite and substantially parallel to thefirst electrode 210. The second electrode 220 preferably has a discshape. In alternative preferred embodiments, the first and secondelectrodes 210 and 220 can assume many other shapes and may be made frommany other materials. Preferably, the separation between the first andthe second electrodes 210 and 220 can be manually or automaticallyadjusted. Preferably, the second electrode 220 is electrically isolatedfrom the chamber housing 202 by an insulator ring 230, which isfabricated from a non-electrically-conductive solid material such asquartz (SiO₂) or alumina (Al₂O₃). A substrate or wafer 232 to be etchedis supported on an interior face or surface of the second electrode 220,which is preferably configured with means for clamping the wafer 232 tothat interior face and means for controlling the temperature of thewafer 232. Such means for clamping and controlling temperature caninclude, but are not limited to, electrostatic clamping and aliquid-cooled second electrode 220 used together with a helium (He) gasdisposed between the wafer 232 and the second electrode 220 to enhancethe thermal conductance between the wafer 232 and the second electrode220. Preferably, a focus ring 234, fabricated of an insulator materialsuch as quartz (SiO₂), is configured about the wafer 232. In alternativepreferred embodiments, the focus ring 234 may be comprised of twosubstantially concentric and proximate rings, an inner ring fabricatedfrom silicon (Si) or silicon carbide (SiC) and an outer ring fabricatedof quartz (SiO₂). In other alternative preferred embodiments, the focusring 234 can have many other shapes and can be made from many othermaterials.

Etchant gas is supplied to the chamber 200 through an etchant gas supply240 and a supply line 242. The supply line 242 is preferably connectedto the chamber 200 through one or more ports passing through the firstelectrode 210, such that the etchant gas is uniformly dispersed withinthe inter-electrode volume 260. Gases are exhausted from the chamber 200and a vacuum pressure is maintained by a vacuum pump 246. Preferably thevacuum pump 246 is connected to the reactor by a vacuum line 244.Preferably, radio frequency (RF) power is supplied to the secondelectrode 220 by an RF power supply 250 coupled to the second electrode220 through an impedance matching network 252.

Preferably, the outer edge of the first electrode 210 projects downwardand forms a cylindrical wall or “shroud” 212 about the inter-electrodevolume 260. Preferably, the shroud 212 has a bottom face portion 262that is substantially adjacent to a face of the focus ring 234 or anupper edge 208 of the chamber 200. Preferably, the bottom face portion262 of the shroud 212 makes electrical contact with the upper edge 208of the chamber 200. Preferably, the electrical connection creates analternate and shorter RF conductive path from the RF power supply 250 toground 254 when compared to the conductive path from the RF power supply250 to ground 254 through the walls 204 of the chamber 200. The shroud212 minimizes electric and magnetic field strength enclosed within anouter chamber volume 206 and improves plasma confinement.

Preferably, the shroud 212 is configured with a plurality of holes orsubstantially vertical slots 214 that completely penetrate or passthrough the shroud 212 and allow the etchant gas within theinter-electrode volume 260 to be exhausted. Preferably, thesubstantially vertical slots 214 are vertically oriented and are about0.8 to about 3.0 millimeters wide. In alternative preferred embodiments,the substantially vertical slots 214 may assume many other shapes andhave many other widths.

The number, shapes, and size of the substantially vertical slots 214 andthickness of the shroud 212 preferably are selected to achieve a desiredgas flow conductance or gas residence time within the inter-electrodevolume 260 and yet, not allow the plasma to become unconfined. In thispreferred embodiment, the substantially vertical slots 214 comprise 180substantially vertical slots about 2.5 millimeters wide by the fulllength of the about 20 millimeter inter-electrode gap. The wall of theshroud 212 is about 6 millimeters thick. In other preferred embodimentsthe number, shape, and size of the openings can vary, as can thethickness of the shroud 212.

At a proper pressure level of etchant gas within the inter-electrodevolume 260 and upon the application of an appropriate RF power to thesecond electrode 220, a plasma is formed within the inter-electrodevolume 260. Preferably, the plasma is confined by the shroud 212 andplasma-surface interactions are restricted to a relatively small and awell-defined area. In exemplary embodiments capable of etching about 200millimeter wafers, the shroud 212 preferably has a height within a rangeof about 14 to about 25 millimeters. The inner diameter (ID) of theshroud 212 is about 220 millimeters inches and an outer diameter (OD) ofthe shroud 212 is about 235 millimeters. The substantially verticalslots 214 have widths of about 2.0 millimeters and lengths of about 12to about 24 millimeters that are spaced about every 2.0 degrees. Inthese exemplary embodiments, the first electrode 210 and a unitaryshroud 212 are comprised of silicon (Si) or silicon carbide (SiC).Moreover, a 3000 Watt 27 MHz RF power supply in combination with a 3000Watt 2 MHz RF power supply was used. In other preferred embodiments,including those embodiments that are capable of etching about 200millimeter and/or about 300 millimeter wafers, the width, the diameters,dimensions of the substantially vertical slots, and the material used tomake the shroud 212 can vary. Moreover, the frequencies and RF powerlevels can also vary.

In operation, the wafer 232 is positioned on an inner surface or face ofthe second electrode 220 as described at act 502 of FIG. 5. At act 504,the chamber 200 is evacuated at act 504. A means for clamping, such as awafer clamping ring or an electrostatic charge, for example, secures thewafer 232 to the second electrode 220. Process gas is supplied throughthe distribution source 240 at act 506. The process gas enters theinter-electrode volume 260 via the gas supply line 242 and adistribution device such as a showerhead. A selected pressure in theinter-electrode volume 260 is attained by controlling the rate ofprocess gas introduction and/or the rate of gas removal. A pump, such asa mechanical vacuum pump (e.g., a turbo pump) removes the process gasfrom the inter-electrode volume 260 via an exhaust port and vacuum line244.

Preferably, RF power is applied to the second electrode 220, whichcreates a high-energy electric field within the inter-electrode volume260 and generates plasma at act 508. Thereafter, the plasma reacts withthe exposed surface of the wafer 232 at act 510. It should be noted thatthe acts illustrated in FIG. 5 may be reordered and/or may includeadditional acts before or after the illustrated acts.

Preferably, the shroud 212 substantially terminates electric fieldsformed within the inter-electrode volume 260, which prevents theelectric fields from penetrating the exterior chamber volume 206. Thesubstantially vertical slots 214 within the shroud 212 allow the processgas to flow with a minimal pressure loss between the inter-electrodevolume 260 and the vacuum line 244, making high gas flow rates at lowprocess pressures attainable.

In some exemplary embodiments, the shroud 212 effectively modifies theelectric fields about the wafer 232 and modifies the process. In someoxide etch applications for example, the shroud 212 increases the etchrate at the outer edge of the wafer 232. One advantage of this preferredembodiment is that an improved etch rate uniformity across the wafer 232can be attained.

Given that the shroud 212 substantially terminates the electric fieldnear the periphery of the inter-electrode volume 260 with a limitedresistance to gas flow, the shroud 212 encompasses any structure thatachieves that function. Accordingly, the shroud 212 is not limited tocontainment structures having only substantially vertical slots 214. Inalternative preferred embodiments, the shroud 212 includes substantiallyhorizontal slots that in some instances are substantially parallel tothe faces or interior surfaces of the first and second electrodes 210and 220. The shroud 212 can also include perforations, gaps, and/or anyother suitable arrangement and combination of holes, slots, gaps,channels, etc., of uniform or non-uniform cross section that allowprocess gas to flow from the inter-electrode volume 260 to the vacuumline 244. Preferably, the shroud 212 achieves a maximum gas conductance.Moreover, since the shroud 212 is at a ground potential, the size of thefirst electrode 210 can be decreased without substantially changing theelectrical state of the plasma formed within the inter-electrode volume260.

From the forgoing description, it should be apparent that the shroud 212may be a unitary part of, or separate from, but electrically coupled to,the first electrode 210. Preferably, the shroud 212 is moveable, meaningthe shroud 212 can be manually or automatically raised or lowered withrespect to the second electrode 220 even while the apparatus and methodare operating. As depicted in FIG. 6, the shroud 212 is physicallyseparate from the first electrode 210 and is mechanically andelectrically connected to a plate 217. Three or more lift pins 218 areattached equally about the plate 217 and facilitate the raising andlowering the shroud 212. Preferably, six or more flexible electricallyconductive straps 219 provide electrical contact between the plate 217and the chamber 200. In the preferred embodiment, when the shroud 212 ismoved to a lowermost position, a lower surface 216 of the shroud 212makes mechanical and electrical contact with the upper edge 208 of thechamber 200. These contacts create an alternate and shorter RF returnpath from the RF power supply 250 to ground 254 when compared to the RFreturn path from the power supply 250 to ground 254 that comprises walls204 of the chamber 200. The shorter conduction path to ground 254minimizes electric and magnetic field strength in the outside chambervolume 206 and improves plasma confinement.

As shown in FIG. 7, the shroud 212 can also be physically separate fromthe first electrode 210 and mechanically and electrically connected to alower half of the chamber 200 near the second electrode 220. Preferably,the lower surface 216 of the shroud 212 is mechanically and electricallycoupled to a conductive ring 213. Preferably, the conductive ring 213 ismechanically and electrically coupled to the upper edge 208 of thechamber 200.

FIG. 8 depicts another alternative preferred embodiment of a shroud 450enclosed within a plasma reactor incorporating two independently RFpowered electrodes. Such reactors can be referred to as “triodes” (2 RFpowered electrodes and a grounded surface). Referring to FIGS. 8, 9, and10, a triode reactor 400 is comprised of a chamber 402, an upperelectrode 410, and a lower electrode 420. Preferably the chamber 402 iselectrically coupled to an electrical ground 448. Preferably, the upperelectrode 410 is electrically isolated from the chamber 402 by an upperinsulator ring 414. The upper electrode 410 preferably has a plate 412of silicon (Si), silicon carbide (SiC), or other suitable materialmechanically and electrically coupled to the chamber 402 interior faces.The upper electrode 410 is coupled to an RF power supply 444 through animpedance matching network 446.

Preferably, the lower electrode 420 is electrically isolated from thechamber 402 by the lower insulator ring 422 and preferably incorporatesmeans for mechanically or electrically holding and cooling a substrateor wafer 424 positioned on the lower electrode 420 interior face thatwere described above. A focus ring 426 comprised of electricallyinsulating material is preferably situated about the wafer 424. RF poweris supplied to the lower electrode 420 by an RF power supply 440 and animpedance matching network 442.

Etchant gas is supplied to the reactor 400 by means of an etchant gassupply 430 and a supply line 432. The supply line 432 is preferablyconnected to the reactor 400 through one or more ports passing throughthe upper electrode 410, such that the etchant gas is delivereduniformly to an inter-electrode volume 460. Gases are exhausted from thereactor 400 and a vacuum level is maintained within the chamber 402 by avacuum pump 434, which is connected to the reactor 400 through a vacuumline 436.

Preferably, the shroud 450 is positioned in an annular space about thelower electrode 420, such that the shroud 450 forms a barrier betweenthe inter-electrode volume 460 and a volume 404 positioned within thelower half of the chamber 402. Preferably, the shroud 450 ismechanically and electrically coupled to the chamber 402 at portionsabout the shroud's 450 inner and outer circumference. Preferably, theshroud 450 includes a plurality of slots or holes 452 through which theprocess gas may pass easily but whose dimensions are sufficient toeffectively terminate all electric fields formed within the plasmavolume 460, such that substantially no electric fields exist in thelower portion 404 of the chamber 402. Preferably, these slots 452 areabout 0.8 to about 3.0 millimeters wide and the shroud 450 is about 6 toabout 12 millimeters thick. The orientation of the slots 452 may extendradially, extend circumferentially, or extend in any other suitabledirection.

As shown in FIGS. 9 and 10, the respective radially andcircumferentially extending slots of the shroud 450 are aligned withradially and circumferential extending slots 456, respectively, of acover plate 454. As shown in FIGS. 9 and 10, the shroud 450 can be aunitary part of the cover plate 454, although in alternative preferredembodiments the shroud 450 and the cover plate 454 can be separatecomponents. Preferably the slots 456 of the cover plate 454 align withthe slots 452 of the shroud 450. Preferably, the cover plate 454 isfabricated from silicon (Si), silicon carbide (SiC) or other suitablematerial.

The foregoing detailed description describes only a few of the manyforms that the present invention can take and should therefore be takenas illustrative rather than limiting. It is only the following claims,including all equivalents that are intended to define the scope of theinvention.

The invention claimed is:
 1. A plasma confinement system comprising: anelectrical ground; a containment device coupled to the electricalground, the containment device acting as a first electrode having asurface facing an interior of the containment device; a process gassource coupled to the containment device; a second electrode having asurface facing the interior of the containment device that is proximateand substantially parallel to the first electrode; a first volumedisposed between the first and the second electrodes; and a secondvolume disposed next to the first volume, wherein the first volume andthe second volume are separated by one side adjacent to both the firstvolume and the second volume; wherein the containment device comprisesthe one side, the containment device substantially enclosing the firstvolume and electrically coupled to the electrical ground, the one sidecomprising at least one channel that allows gas to pass between thefirst volume and second volume, wherein the at least one channel isconfigured to maintain a pressure level of at least one of the firstvolume and the second volume.
 2. The plasma confinement system of claim1 wherein the at least one channel is configured to minimize a pressureloss between the first volume and the second volume.
 3. The plasmaconfinement system of claim 2 further comprising a vacuum pump coupledwith the second volume, wherein the second volume comprises an outerchamber volume that is coupled with the vacuum pump through a vacuumline, wherein the vacuum pump is configured to remove gas from theplasma confinement system.
 4. The plasma confinement system of claim 1wherein the containment device comprises electrically conductiveportions that substantially confine electric fields to the first volume.5. The plasma confinement system of claim 1 further comprising a supplyline configured to channel the process gas into the first volume fromthe process gas source.
 6. The plasma confinement system of claim 1wherein the at least one channel is configured to equalize a pressurebetween the first volume and the second volume.
 7. A plasma chambersystem comprising: a process gas source; a shroud that receives processgas from the process gas source, wherein the shroud comprises a firstelectrode; an inter-electrode volume that is disposed within the shroud,wherein the first electrode has a surface facing an interior of theinter-electrode volume; a second electrode having a surface facing theinterior of the inter-electrode volume that is proximate andsubstantially parallel to the first electrode, wherein theinter-electrode volume is disposed between the first electrode and thesecond electrode; a second volume abutting the interelectrode volume;and at least one channel in the shroud that allows gas to pass betweenthe inter-electrode volume and second volume, wherein the at least onechannel is configured to minimize a pressure loss between theinter-electrode volume and the second volume.
 8. The system of claim 7wherein the shroud substantially terminates electric fields formedwithin the inter-electrode volume to prevent the electric fields frompenetrating the second volume.
 9. The system of claim 7 wherein theshroud comprises electrically conductive portions that substantiallyconfine electric fields to the inter-electrode volume.
 10. The system ofclaim 7 wherein the shroud encloses the inter-electrode volume on threesides.
 11. The system of claim 10 wherein the first electrode comprisesone side of the shroud and protrudes into the inter-electrode volume.12. The system of claim 7 wherein the second volume comprises an outerelectrode volume.
 13. The system of claim 7 further comprising a vacuumpump that removes the process gas.
 14. The system of claim 13 furthercomprising a vacuum line connecting the vacuum pump with second volume.15. A plasma chamber apparatus comprising: a gas source; a firstelectrode; a second electrode that is proximate to and substantiallyparallel to the first electrode; an inter-electrode volume between aninner surface of the first electrode and an inner surface of the secondelectrode that receives gas from the gas source; a second volumeseparate from but connected with the interelectrode volume; wherein thefirst electrode comprises a wall that separates the inter-electrodevolume from the second volume, wherein the inter-electrode volume isadjoining the second volume at the wall; at least one channel throughthe wall that allows gas to pass between the inter-electrode volume andsecond volume, wherein the at least one channel is configured tomaintain a pressure level at the inter-electrode volume or the secondvolume.
 16. The plasma chamber apparatus of claim 15 wherein the wallcomprising at least one channel substantially terminates electric fieldsformed within the inter-electrode volume from penetrating the secondvolume.
 17. The plasma chamber apparatus of claim 15 wherein the wallcomprises an outer edge of the first electrode that projects about theinter-electrode volume.
 18. The plasma chamber apparatus of claim 15wherein the first electrode comprises a shroud that at least partiallyencloses the inter-electrode volume.
 19. The plasma chamber apparatus ofclaim 15 wherein the second volume comprises an outer electrode volume.20. The plasma chamber apparatus of claim 19 further comprising a vacuumpump connected with the outer electrode volume through a vacuum line,wherein the vacuum pump is configured to remove gas from the plasmachamber apparatus.
 21. The plasma chamber apparatus of claim 15 whereinthe wall comprises a partition between the inter-electrode volume andthe second volume.